This project investigated the effects that different rates of nitrogen fertigation had on red drupelet disorder expression in commercial blackberries. Red drupelet disorder (sometimes known as red drupelet reversion or reddening) is a postharvest physiological disorder that causes fruit, which is black at harvest, to revert to a red colour following cold storage. This causes a mottled appearance on the fruit that is off-putting to the consumer and can render fruit unmarketable in some cases, causing significant financial loss to producers. In severe cases, the disorder can affect over half the crop. There is currently very little knowledge surrounding causes and contributing factors to the disorder, with no standard management practices available to reduce incidence. One factor that has previously been suggested as a contributor to high rates of the disorder is excess nitrogen fertilisation close to harvest.Results showed that higher nitrogen fertigation rates prior to and during harvest, to canes grown under high tunnels, significantly increased rates of red drupelet disorder in fruit. The highest nitrogen application rate used in the study resulted in a 56% increase in expression of red drupelet compared with the lowest application rate throughout the course of the harvest season. This effect was highest at the beginning of the harvest season, at which time red drupelet incidence was highest, and declined as the harvest season progressed. Higher nitrogen rates also increased the total yield, but did not affect berry weight, pH, sugar content, or total acidity. This research shows that a link exists between nitrogen fertigation rates and red drupelet disorder expression, although further work is ongoing to investigate the underlying reason for this increase. These findings have the potential to guide industry standards to reduce incidence of the disorder in commercially produced blackberries.

Max Edgley won an ISHS student award for the best oral presentation at the I International Symposium on Protected Cultivation in Tropical and Temperate Climates & X International Symposium on Protected Cultivation in Mild Winter Climates in Australia in November 2016.